Patent GB-394686-A (GB)
Title: Improvements in or relating to voltage failure protection devices
IPC: H01H71/44
Filed: 1931-12-30
Abstract: 394,686. Protective cut-out arrangements. IGRANIC ELECTRIC CO., Ltd., 147, Queen Victoria Street, London, and WRIGHT, S. R., 113, London Road, Bedford. Dec. 30, 1931, No. 35980. [Class 38 (v).] Electromagnetic switches; switches, latching and unlatching; retarding devices.-A voltagefailure protection device for polyphase circuits comprises three no-volt coils 12 having independently movable plungers 13 and magnetic plates 3, 8 to complete the magnetic circuits through the plungers, the arrangement being that if all the plungers move to the non- attracted position simultaneously, as by switching off, no response occurs, but if any one plunger moves to the non-attracted position, as by phase-failure, the device responds. Fig. 1 shows an " exploded " view of one form, in which the plate 3 insulatingly carries fixed contacts 1, the outer faces of which are engaged normally by contacts 2a on the bridging member 2 which is attached to the insulating plate 4. Apertures 16 in the latter and 15 in the plate 3 permit the passage of extensions 14 of the plungers 13, weights 17 being fitted to the extensions 14 so as, when the coils 12 are energized, to be lifted clear of the plate 4, but to fall thereon when the coils are de-energized. The plate 4 is also apertured at 11 to receive a pin 10 with a certain amount of play, the base of pin 10 and the contacts 1 normally forming a three-point, triangular support for plate 4, with freedom for the latter to pivot about any one of those points and separate one or both contacts 2a from the corresponding fixed contacts. Such pivoting occurs when any one plunger falls and causes its weight 17 to strike the plate 4, but if all the plungers fall owing to switching off, the plate 4 remains still in the position in which it is normally biased by the overload armature 8, the insulating rod 5 of which carries a collar 5a passing over the top of a hole 7. When the plate 4 tilts owing to voltage failure in one phase, the armature 8 is lifted slightly by rod 5 against the retarding action of a dashpot 9. At the same time this lifting is assisted by the coils 12 attracting the armature 8, the attraction being a measure of the current and so reducing the retarding action on heavy loads. On overload, the armature 8 is attracted and by means of a collar 5b lifts the plate 4 and opens the contacts 1, 2, the action being preferably slow for moderate overloads and instantaneous for heavy overloads, as by means of the connection disclosed in Specification 370,122. A locking-out arrangement may be employed to prevent automatic resetting of plate 4 when the other two plungers 13 fall on opening the main circuit. Numerical data are set out in the Specification, which also describes the arrangement of the magnetic circuits for three and two-phase working. Figs. 6, 7 show a modified arrangement of contacts according to which the bridging member is slotted in two places at 19 for engagement with pins 20, and carries contacts 2a engaging (in Fig. 7) with fixed contacts 1. Pivoted at 23 are three bell-crank levers 21 having horizontal arms extending each under its appropriate weight 17 and vertical arms which bear, the back one on one side, and the front ones on the other side, of the member 4. When the back plunger, Fig. 7, falls, its lever 21 moves the member 4 bodily forward to disengage contacts 2a from 1. If one of the front plungers falls, its lever 21 rotates 4 about the nearer pin 20, disengaging the contacts as before. The member 4 is reset by a handoperated button 24 and an extension 21a of the rear lever 21 is engageable by the overload element 5 to separate the contacts on overload.